1. Field of the Invention
The present invention relates to an inherently tuned antenna having circuit portions which provide regenerative feedback into the antenna such that the antenna's effective area is substantially greater than its physical area and, more specifically, it provides such circuits which are adapted to be employed in miniaturized form such as on an integrated circuit chip or die. Associated methods are provided.
2. Description of the Prior Art
It has long been known that energy such as RF signals can be transmitted through the air to various types of receiving antennas for a wide range of purposes.
Rudenberg in “Der Empfang Elektricscher Wellen in der Drahtlosen Telegraphie” (“The Receipt of Electric Waves in the Wireless Telegraphy”) Annalen der Physik IV, 25, 1908, pp. 446-466 disclosed the fact that regeneration through a non-ideal tank circuit with a ¼ wavelength whip antenna can result in an antenna having an effective area larger than its geometric area. He discloses use of the line integral length of the ¼ wavelength whip to achieve the effective area. He stated that the antenna interacts with an incoming field which may be approximately a plane wave causing a current to flow in the antenna by induction. The current, which may be enhanced by regeneration, produces a field in the vicinity of the antenna, with the field interacting with the incoming field in such a way that the incoming field lines are bent. The field lines are bent in such a way that energy is caused to flow from a relatively large portion of the incoming wavefront having the effect of absorbing energy from the wavefront into the antenna from an area of the wavefront which is much larger than the geometric area of the antenna. See also Fleming “On Atoms of Action, Electricity, and Light,” Philosophical Magazine 14, p. 591 (1932); Bohren, “How Can a Particle Absorb More Than the Light Incident On It?”, Am. J. Phys. 51, No. 4, p. 323 (1983); and Paul, et al., “Light Absorption by a Dipole,” Sov. Phys. Usp. 26, No. 10, p. 923 (1983) which elaborate on the teachings of Rudenberg. These teachings were all directed to antennas that can be modeled as tuned circuits or mathematically analogous situations encountered in atomic physics.
Regeneration was said to reduce the resistance of the antenna circuit, thereby resulting in increased antenna current and, therefore, increased antenna-field interaction to thereby effect absorption of energy from a larger effective area of the income field. These prior disclosures, while discussing the physical phenomenon, do not teach how to achieve the effect.
U.S. Pat. No. 5,296,866 discloses the use of regeneration in connection with activities in the 1920's involving vacuum tube radio receivers, which consisted of discrete inductor-capacitor tuned circuits coupled to a long-wire antenna and to the grid circuit of a vacuum triode. Some of the energy of the anode circuit was said to be introduced as positive feedback into the grid-antenna circuit. This was said to be like introduction of a negative resistance into the antenna-grid circuit. For example, wind-induced motion of the antenna causing antenna impedance variation were said to be the source of a lack of stability with the circuit going into oscillation responsive thereto. Subsequently, it was suggested that regeneration be applied to a second amplifier stage which was isolated from the antenna circuit by a buffer tube circuit. This was said to reduce spurious signals, but also resulted in substantial reduction of sensitivity. This patent contains additional disclosures of efforts to improve the performance through introduction of negative inductive reactants or resistance with a view toward effecting cancellation of positive electrical characteristics. Stability, however, is not of importance in energy harvesting for conversion to direct current or contemplated by the present invention.
This patent discloses the use of a separate tank circuit, employs discrete inductors, discrete capacitors to increase effective antenna area.
U.S. Pat. No. 5,296,866 also discloses the use of positive feedback in a controlled manner in reducing antenna circuit impedance to thereby reduce instability and achieve an antenna effective area which is said to be larger than results from other configurations. This patent, however, requires the use of discrete circuitry in order to provide positive feedback in a controlled manner. With respect to smaller antennas, the addition of discrete circuit components to provide regeneration increases complexity and costs and, therefore, does not provide an ideal solution, particularly in respect to small, planar antennas on a substrate such as an integrated circuit chip such as a CMOS chip, for example.
There is current interest in developing smaller antennas that can be used in a variety of small electronic end use applications, such as cellular phones, personal pagers, RFID and the like, through the use of planar antennas formed on substrates, such as electronic chips. See generally U.S. Pat. Nos. 4,598,276; 6,373,447; and 4,857,893.
U.S. Pat. No. 4,598,276 discloses an electronic article surveillance system and a marker for use therein. The marker includes a tuned resonant circuit having inductive and capacitive components. The tuned resonant circuit is formed on a laminate of a dielectric with conductive multi-turned spirals on opposing surfaces of the dielectric. The capacitive component is said to be formed as a result of distributive capacitance between opposed spirals. The circuit is said to resonate at least in two predetermined frequencies which are subsequently received to create an output signal. There is no disclosure of the use of regeneration to create a greater effective area for the tuned resonant circuit than the physical area.
U.S. Pat. No. 6,373,447 discloses the use of one or more antennas that are formed on an integrated circuit chip connected to other circuitry on the chip. The antenna configurations include loop, multi-turned loop, square spiral, long wire and dipole. The antenna could have two or more segments which could selectively be connected to one another to alter effective length of the antenna. Also, the two antennas are said to be capable of being formed in two different metalization layers separated by an insulating layer. A major shortcoming of this teaching is that the antenna's transmitting and receiving strength is proportional to the number of turns in the area of the loop. There is no disclosure of regeneration to increase the effective area.
U.S. Pat. No. 4,857,893 discloses the use of planar antennas that are included in circuitry of a transponder on a chip. The planar antenna of the transponder was said to employ magnetic film inductors on the chip in order to allow for a reduction in the number of turns and thereby simplify fabrication of the inductors. It disclosed an antenna having a multi-turned spiral coil and having a 1 cm×1 cm outer diameter. When a high frequency current was passed in the coil, the magnetic films were said to be driven in a hard direction and the two magnetic films around each conductor serve as a magnetic core enclosing a one turn coil. The magnetic films were said to increase the inductance of the coil, in addition to its free-space inductance. The use of a resonant circuit was not disclosed. One of the problems with this approach is the need to fabricate small, air core inductors of sufficiently high inductance and Q for integrated circuit applications. The small air core inductors were said to be made by depositing a permalloy magnetic film or other suitable material having a large magnetic permeability and electric insulating properties in order to increase the inductance of the coil. Such an approach increases the complexity and cost of the antenna on a chip and also limits the ability to reduce the size of the antenna because of the need for the magnetic film layers between the antenna coils.
Co-pending U.S. patent application Ser. No. 09/951,032, which is expressly incorporated herein by reference, discloses an antenna on a chip having an effective area 300 to 400 times greater than its physical area. The effective area is enlarged through the use of an LC tank circuit formed through the distributed inductance and capacitance of a spiral conductor. This is accomplished through the use in the antenna of inter-electrode capacitance and inductance to form the LC tank circuit. This, without requiring the addition of discrete circuitry, provides the antenna with an effective area greater than its physical area. It also eliminates the need to employ magnetic film. As a result, the production of the antenna on an integrated circuit chip is facilitated, as is the design of ultra-small antennas on such chips. See also U.S. Pat. No. 6,289,237, the disclosure of which is expressly incorporated herein by reference.
Despite the foregoing disclosures, there remains a very real and substantial need for circuits useful in receiving and transmitting energy in space, which circuits provide a substantially greater effective area than their physical area. There is a further need for such a system and related methods which facilitate the use of inherently tuned antennas and distributed electrical properties to effect use of antenna regeneration technology in providing such circuits on an integrated circuit chip.